It is commonplace in drilling for oil and gas, to use fluids such as brines as well servicing fluids. In general, such fluids have desirably a high density. In particular, highly concentrated alkali metal salts of carboxylic acids have been developed for use in oil and gas well drilling and completion operations. Such a fluid may be based upon cesium and potassium salts such as formates, which can provide brines of specific gravity values of 1.6 to 2.3, depending upon solution concentrations.
During use of such brines, they may be contaminated with sodium chloride from sea water or from water or salt entrained within the rock and mud during application in the well bore. Chloride ions can cause severe corrosion of steel pipework and additionally may be incompatible with the rock matrix, causing damage to or near the well bore area. Such problems may result in users of such brines refusing to re-use chloride-contaminated brines. A charge of cesium formate solution for use as an oil field brine may cost in the order of $10M, so there is considerable need to improve the prospects for recycling such a brine.
Further, if a diluted brine is returned to high density by evaporation of water, any chloride concentration will increase by this process, thereby rendering the brine less suitable for re-use.